1. Field of the Invention.
The present invention relates to improved methods and compositions for sealing subterranean zones.
2. Description of the Prior Art
In the drilling of oil and gas wells using the rotary drilling method, drilling fluid is circulated through the drill string and drill bit and then back to the surface by way of the well bore being drilled. The drilling fluid maintains hydrostatic pressure on the subterranean zones through which the well bore is drilled and circulates cuttings out of the well bore. During such drilling, subterranean vugs, fractures and other thief zones are often encountered whereby the drilling fluid circulation is lost and drilling operations must be terminated while remedial steps are taken. Also, when a subterranean zone is penetrated containing fluids under pressure which exceeds the hydrostatic pressure exerted on the zone by the drilling fluid, formation fluid crossflows and/or underground blow-outs can and often do occur.
Heretofore, a variety of compositions have been developed and used for combatting lost circulation, crossflow and underground blow-out problems. However, such compositions have often been unsuccessful due to delayed and inadequate viscosity development by the compositions. For example, a variety of compositions containing hydraulic cement or the like have been used in attempts to stop lost circulation. The lost circulation is usually the result of encountering weak subterranean zones that contain natural fractures or are fractured by drilling fluid pressures and rapidly break down. When a cement or other slow setting composition is squeezed into the zone, the delay in developing high viscosity allows the cement composition to be diluted and displaced into the zone whereby it bypasses the fractures and vugs causing the lost circulation. The same type of problem often occurs when cross-linked hydrated gels and other similar plugging compositions are utilized.
Thus, there are needs for improved methods and compositions for sealing subterranean zones whereby the compositions have high viscosity when placed and simultaneously or very shortly thereafter set into rigid masses which effectively seal the subterranean zones.